'World with just girls in it': Shocking new study reveals Y chromosome is disappearing

Recent research has spotlighted an intriguing and somewhat concerning trend: the Y chromosome, crucial for determining male sex, is gradually disappearing. This raises questions about the future of male offspring and the potential implications for human evolution.

What is the Y Chromosome and How Does It Determine Sex?

In mammals, including humans, males and females have different sets of sex chromosomes. Females have two X chromosomes (XX), while males have one X and one much smaller Y chromosome (XY). Despite its small size, the Y chromosome carries the SRY gene, which is essential for developing male characteristics. Around 12 weeks after conception, the SRY gene activates a series of genetic processes leading to the formation of testes.

These testes then produce testosterone, which directs the embryo to develop as male. Discovered in 1990, the SRY gene triggers the SOX9 gene, which is critical for male development in all vertebrates. Although SOX9 is not on the sex chromosomes, it relies on the SRY gene to activate it.

Why is the Y Chromosome Disappearing?

Over the past 166 million years, since humans and platypuses branched off from a common ancestor, the Y chromosome has significantly reduced in size. It has shrunk from containing 900 active genes to just 55. This represents a loss of about five genes per million years. If this trend continues, the Y chromosome might disappear completely within the next 11 million years.

In contrast, the X chromosome has around 900 genes with various functions, while the Y chromosome has only 55 genes, 27 of which are specific to males. Much of the Y chromosome is made up of repetitive 'junk DNA,' which makes it prone to instability and potential extinction.

Credit: ANI/ Y chromosome shrinking

Implications for the Future of Human Reproduction

The disappearance of the Y chromosome could have profound implications for human reproduction. One potential outcome is the evolution of new sex-determining systems. Professor Graves has noted that this evolution could lead to multiple sex-determining mechanisms developing in different regions, possibly resulting in separate human species.

Currently, some species of lizards and snakes are female-only and reproduce through parthenogenesis, where eggs are produced from their own genes. However, this process isn¡¯t feasible for humans due to the need for at least 30 crucial genes that come only from the father. If the Y chromosome were to disappear, it could potentially end human reproduction as we know it.

Despite these concerns, some experts believe that the Y chromosome might not vanish completely. A 2017 study in PLOS Genetics suggests that the chromosome has defense mechanisms in place, such as palindromic DNA sequences and repetitive gene copies. These features could help repair damaged genes and slow down the chromosome's degradation.

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